NEC Questions and Answers based on 2020 NEC^® - August 2021

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For EC&M Magazine
By Mike Holt, NEC^® Consultant
Here's the follow-up to yesterday's newsletter. This includes the answers to the questions sent, so you can see how you did.

Note: The answers to these questions are based on the 2020 NEC.

Q1. What are the Code rules for securing and supporting Type LFMC?
A1. LFMC must be securely fastened in place and supported in accordance with (A) and (B) [350.30].
(A) Securely Fastened. LFMC must be securely fastened by a means approved by the
authority having jurisdiction within 1 ft of termination and must be secured and supported at intervals not exceeding 4½ ft.

Where cable ties are used for securing LFMC they must be listed and identified for securement and support.

Ex 1: LFMC is not required to be securely fastened or supported where fished between access points through concealed spaces and supporting is impracticable. 

Ex 2: If flexibility is necessary after installation, unsecured lengths from the last point where the raceway is securely fastened are not permitted to exceed:
(1) 3 ft for trade sizes ½ through 1¼
(2) 4 ft for trade sizes 1½ through 2
(3) 5 ft for trade sizes 2½ and larger

Ex 4: Lengths not exceeding 6 ft from the last point where the raceway is securely fastened can be unsecured within an accessible ceiling for a luminaire(s) or other equipment.  Figure 01

For the purposes of these exceptions, listed LFMC fittings are permitted as a means of securement and support. 

Author’s Comment:
►This last sentence following the four exceptions means that, the use of LFMC fittings as the means of securing and supporting, only applies to installations made using one of the four exceptions. It should not be misconstrued as blanket permission to use the fittings to secure and support the LFMC in all applications.

Q2. What does the Code require to compensate for thermal expansion of a cable tray?
A2. Expansion splice plates for cable trays must be provided where necessary to compensate for thermal expansion and contraction [392.44].

Author’s Comment:
►Thermal expansion is an issue without the installation of raceway expansion joints and is often overlooked. In order for the raceway to properly serve its function, it must be able to expand, as well as contract, and expansion joints provide the ability to do so.
►This Code section gives no guidance as to how to determine the need for an expansion splice plate but there is a National Electrical Manufacturer’s Association (NEMA) document available as a free download that may assist. This document is titled; “NEMA VE2, Cable Tray Installation Guidelines.”

Q3. What is required by the NEC where conductors transition from a cable tray to raceways or enclosures?
A3. Bushed Conduit and Tubing [392.46]
A box is not required where cables or conductors are installed in a bushed raceway used for support, for protection against physical damage or where conductors or cables transition to a raceway from the cable tray.

(A) Through Bushed Conduit or Tubing. Individual conductors or multiconductor cables with entirely nonmetallic sheaths, can enter enclosures where they are terminated through nonflexible bushed conduit or tubing installed for their protection, provided they are secured at the point of transition from the cable tray and the raceway is sealed at the outer end using an approved means so as to prevent debris from entering the equipment through the raceway. 

(B) Flanged Connections. Individual conductors or multiconductor cables with entirely nonmetallic sheaths, can enter enclosures through openings associated with flanges from cable trays where the cable tray is attached to the flange and the flange is mounted directly to the equipment. The openings must be made such that the conductors are protected from abrasion and the openings must be sealed or covered to prevent debris from entering the enclosure through them.

Informational Note: One method of preventing debris from entering the enclosure is to seal the outer end of the raceway or the opening with duct seal.

Q4. The NEC does not permit flexible cords and flexible cables to be used for what purposes?
A4. Uses Not Permitted [400.12]
Unless specifically permitted in 400.10, flexible cords, flexible cables, cord sets (extension cords), and power-supply cords are not permitted for the following: 
(1) Flexible cords, flexible cables, cord sets (extension cords), and power-supply cords are not permitted to be a substitute for the fixed wiring.

(2) Flexible cords, flexible cables, cord sets (extension cords), and power-supply cords are not permitted to be run through holes in walls, structural ceilings, suspended or dropped ceilings, or floors.

(3) Flexible cords, flexible cables, cord sets (extension cords), and power-supply cords are not permitted to be run through doorways, windows, or similar openings.

(4) Flexible cords, flexible cables, cord sets (extension cords), and power-supply cords are not permitted to be attached to building surfaces.

Ex to (4): Flexible cords and flexible cables used for temporary wiring [590.4] may be attached to building surfaces.

(5) Flexible cords, flexible cables, cord sets (extension cords), and power-supply cords are not permitted to be concealed by walls, floors, or ceilings, or located above suspended or dropped ceilings. 

Ex to (5): Flexible cords, flexible cables, and power-supply cords are permitted if contained within an enclosure for use in other spaces used for environmental air as permitted by [300.22(C)(3)].

(6) Flexible cords, flexible cord sets (extension cords), and power-supply cords are not permitted to be installed in raceways, except as permitted by 400.17 for industrial establishments where the conditions of maintenance and supervision ensure that only qualified persons will service the installation.

(7) Flexible cords, flexible cord sets (extension cords), and power-supply cords are not permitted where they are subject to physical damage. 

Author’s Comment:
►It remains unclear how the uses not permitted can apply to cord sets and power-supply cords since they are not included in the scope of Article 400.

Q5. What manner of protection is required by the Code for flexible cords when passing through holes in covers, outlet boxes, or similar enclosures?
A5. Flexible cords and flexible cables must be protected by bushings or fittings where passing through holes in covers, outlet boxes, or similar enclosures [400.17].